Using upper case literal suffixes removes the potential ambiguity between "1" (digit 1) and "l" (letter el) for declaring literals.
long long1 = 1l; // Noncompliant float float1 = 1.0f; // Noncompliant double double1 = 1.0d; // Noncompliant
long long1 = 1L; float float1 = 1.0F; double double1 = 1.0D;